Projected levels of climate change would exacerbate
the continuation of land degradation and desertification that has occurred
over the past few centuries in many areas. Land-use conversion
and the intensive use of land, particularly in the world's arid and
semi-arid regions, has resulted in decreased soil fertility and increased
land degradation and desertification. The changes have been large enough
to be apparent from satellite images. Land degradation already affects
more than 900 million people in 100 countries, and one quarter of the
world soil resources, most of them in the developing countries. The annual
recorded losses of millions of hectares significantly undermine economies
and create some irreversible situations. The TAR projections using the
SRES scenarios indicate increased droughts, higher intensity of rainfall,
more irregular rainfall patterns, and more frequent tropical summer drought
in the mid-latitude continental interiors. The systems that likely would
be impacted include those with scarce water resources, rangelands, and
land subsidence (see Table 8-2).

Irreversible losses of biodiversity could be accelerated with climate
change.
Significant extinctions of plant and animal species are projected
and would impact rural livelihoods, tourism, and genetic resources
(medium confidence).

Decreases in agricultural productivity and aquaculture due to thermal
and water stress, sea-level rise, floods and droughts, and tropical
cyclones would diminish food security in many countries of arid, tropical,
and temperate Asia; agriculture would expand and increase in productivity
in northern areas (medium confidence). Climate change would
exacerbate threat to biodiversity due to land-use and land-cover change
and population pressure (medium confidence). Sea-level rise
would put ecological security at risk including mangroves and coral
reefs (high confidence).

A warming of 1ºC would threaten the survival of species currently
near the upper limit of their temperature range, notably in marginal
alpine regions.
Some species with restricted climatic niches and that are unable to
migrate due to fragmentation of the landscape soil differences or
topography could become endangered or extinct (high confidence).
Australian ecosystems that are particularly vulnerable to climate
change include coral reefs, arid and semi-arid habitats in southwest
and inland Australia, and Australian alpine systems.
Freshwater wetlands in coastal zones in both Australia and New Zealand
are vulnerable, and some New Zealand ecosystems are vulnerable to
accelerated invasion by weeds.

Natural ecosystems will change due to increasing temperature and
atmospheric concentration of CO2. Diversity in nature reserves
is under threat of rapid change. Loss of important habitats (wetlands,
tundra, and isolated habitats) would threaten some species, including
rare/endemic species and migratory birds. There will be some broadly
positive effects on agriculture in northern Europe (medium confidence);
productivity will decrease in southern and eastern Europe (medium
confidence).

It is well-established that Latin America accounts for one of the
Earth's largest concentrations of biodiversity and the impacts
of climate change can be expected to increase the risk of biodiversity
loss (high confidence). Yields of important crops are projected
to decrease in many locations even when the effects of CO2
are taken into account; subsistence farming in some regions could
be threatened (high confidence).

There is strong evidence that climate change can lead to the loss
of specific ecosystem types (e.g., high alpine areas and specific
coastal (salt marshes and inland prairie "potholes") wetlands)
(high confidence). Some crops would benefit from modest warming
accompanied by increasing CO2, but effect would vary among
crops and regions (high confidence), including declines due
to drought in some areas of Canada's Prairies and the U.S. Great
Plains, potential increased food production in areas of Canada north
of current production areas, and increased warm temperate mixed forest
production (medium confidence). However, benefits for crops
would decline at an increasing rate and possibly become a net loss
with further warming (medium confidence). Unique natural
ecosystems such as prairie wetlands, alpine tundra, and coldwater
ecosystems will be at risk and effective adaptation is unlikely (medium
confidence).

In the Antarctic projected climate change will generate impacts
that will be realized slowly (high confidence). Warmer temperatures
and reduced ice extent are likely to produce long-term changes in
the physical oceanography and ecology of the Southern Ocean, with
intensified biological activity and increased growth rate of fish.

Projected future climate change and sea-level rise will affect shifts
in species composition and competition. It is estimated that one out
of every three (30%) known threatened plants are island endemics,
while 23% of bird species are threatened. Coral reefs, mangroves,
and seagrass beds that often rely on stable environmental conditions
will be adversely affected by rising air and sea temperatures and
sea-level rise (medium confidence). Declines in coastal ecosystems
would negatively impact reef fish and threaten reef fisheries (medium
confidence).

Figure 8-2: This figure shows linkages between
climate change and other environmental factors in food supply and demand.
Increasing food demand by a growing world population calls for larger
food production. This, in turn, brings a series of implications in the use
of land, such as converting wildlands to croplands (extensification), and
using chemical fertilizers and/or using irrigation to increase yield (intensification)
or enabling cultivation in otherwise non-usable land. Expanding the land
under cultivation results in loss of biodiversity, as ecosystems are converted
to fields growing only a few species (usually exotics). Change of forests
to agriculture brings a net loss of carbon to the atmosphere, as forests
are replaced by grassland or cropland. This clearing also increases flooding
probability, as the agricultural systems retain less precipitation than
forests. Intensification of crop production can involve a variety of chemical
treatments, most of them being nitrogen fertilizers bringing the side effect
of release of nitrogen gas compounds (some of which are strong greenhouse
gases) to the atmosphere and nitrogen runoff into watersheds, with many
environmental and health implications. The expansion of irrigation affects
the supply of freshwater for other uses, leading to shortages and conflicts
over water-use rights. Meeting the needs for increased agricultural production
has the potential to increase global rates of biodiversity loss, climate
change, and desertification. There are interrelations, particularly to water,
that underly all these issues, but for simplicity are not shown in the figure.